§ SQL兼容性 - 子查询无别名
§ 1. 语法
greatsql> SELECT * FROM (SELECT 1 FROM DUAL), (SELECT 2 FROM DUAL);
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即在子查询SQL语句中，无需加上别名而不会报语法错误。
§ 2. 示例
greatsql> SELECT * FROM (SELECT 1 FROM DUAL), (SELECT 2 FROM DUAL);
+---+---+
| 1 | 2 |
+---+---+
| 1 | 2 |
+---+---+
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这个SQL请求如果是放在MySQL中执行，则会报告错误：
greatsql> SELECT * FROM (SELECT 1 FROM DUAL), (SELECT 2 FROM DUAL);
ERROR 1248 (42000): Every derived table must have its own alias
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